The present invention relates to a superconducting contact structure formed by an oxide superconductor and a metal superconductor in a superconductor IC or the like.
An oxide represented by yttrium-barium-copper oxide (YBCO) as described in Physical Review Letters, Vol. 58, P. 908 serves as a superconductor at a relatively high critical temperature. YBCO as a superconductor has a critical temperature of 97 K. A circuit combining this oxide superconductor and a metal superconductor represented by niobium may be arranged. In this case, a superconducting contact between these two superconductor materials must be established.
FIG. 1 shows a typical conventional example of a superconducting contact structure made of two metal superconductors. A superconductor 14 is brought into contact with a superconductor 12 through a contact hole in an insulating film 13, thereby establishing a superconducting contact.
A critical, largely anisotropic, superconducting current in YBCO is described in Japanese Journal of Applied Physics, Vol. 26, P. L1248. The superconducting critical current density in a direction perpendicular to the layer is about one percent of that in a direction parallel to the layer. When an oxide superconductor is formed so that the layer is parallel to a substrate 11, it is necessary to supply a large amount of current in a direction parallel to the substrate 11. A small superconducting current is not supplied in the vertical direction, and therefore good superconducting contact cannot be obtained. In order to prevent a decrease in the critical current density, the contact area is 100 times the cross-sectional area of the superconductor 12. However, such a large contact hole is not preferable in view of a need to make things smaller in order to achieve a greater; integration density.